The present invention relates to a continuous process for transforming, by chemico-physical reactions inside molten slag, materials to be gasified, thermally destroyed, inertized or from which elements of commercial value are to be recovered, yielding controlled composition products, and to an apparatus apt to carry out such process.
In particular, the present invention relates to a process and to an apparatus substantially made of a reaction chamber, called reactor, for the continuous transforming by chemico-physical reactions inside molten slag of solid, liquid and gaseous material, even of scrap, yielding controlled composition products at the output of the apparatus itself, avoiding difficult to recycle and/or harmful by-products.
The process object of the present invention is a continuous process for transforming, by chemico-physical reactions inside molten slag, solid, liquid or gaseous materialxe2x80x94even scrap, to be gasified, thermally destroyed, inertized or from which elements of commercial value are to be recovered, yielding controlled composition products, carried out in an apparatus made of an individual reaction chamber, called reactor, having a substantially cylindrical symmetry, including two portions, a top one and a bottom one, communicating and functionally distinct therebetween for carrying out the process, said process being characterised in that it comprises the steps of:
possibly, introducing in the top portion of the reactor, through a first injection level, a comburent gas for the post-combustion of the process gases;
introducing in the bottom portion of the reactor, sideways through a second injection level and/or vertically from the top thereof, the material to be transformed, the fuel, the comburent, and possibly slag inoculants and additives and material-carrying gases;
possibly, introducing inert stirring gases from the reactor bottom;
extracting the process the gases from the top portion of the reactor; and
tapping the transformed material of controlled composition and the inert slag from the bottom portion of the reactor.
The introduction into the bottom portion of the reactor of the material to be transformed, the fuel, the comburent, the possible inoculants and additives and the material-carrying gases can be carried out sideways or vertically from the top thereof. The sideways introduction into the bottom portion of the material to be transformed, together with the fuel, the comburent and the additives, can also be carried out in the radial direction through a plurality of inlets, possibly on different levels.
In an embodiment of the present invention, the material to be transformed, the fuel, a fraction of the comburent, the possible inoculants, additives and material-carrying gases, are introduced into the reactor towards the slag core by horizontal or downwards-slanting injection, and, concomitantly, the remaining comburent fraction is introduced therein with injectors at an upper level.
The material to be transformed may have a granulometry lower than 8 mm.
The granulometry of the fuel and of the additives may be lower than 3 mm.
The injection rate of the comburent into the top portion is lower than 40 m/s, and anyhow such as to allow the individual jets to intermingle thereamong, an effective combustion of the process gas inletted from the bottom portion of the reactor, and the yield of a heat transfer efficiency (THE) greater than 70% between the gas and the molten metal bath.
In embodiments of the process according to the invention the binary basicity index of the slag is greater than 1.
The formation of a slag phase/metal phase emulsion in the bottom portion of the reactor for attaining an efficient heat transfer and elevated reaction kinetics may also be carried out with the injection of stirring gas from the reactor bottom, the power provided by the stirring gas being lower than 2.5 kW per ton of molten metal bath.
The internal pressure of the reactor may range from 1 to 4 bars.
A further subject-matter of the invention is an apparatus for the continuous transforming, by chemico-physical reactions inside molten slag, of materials to be gasified, thermally destroyed, inertized, or from which elements of commercial value are to be recovered, yielding controlled composition products, characterised in that it comprises:
a reaction chamber, called reactor, having a substantially cylindrical symmetry, including two portions, a top and a bottom one, communicating and functionally distinct therebetween for carrying out the process;
a substantially frustoconical-shaped connector, between the top portion of the reactor and a flue gas ejection conduit;
means for feeding, into the bottom portion of the reactor, the material to be transformed, the fuel, possibly the slag inoculants and additives, and the material-carrying gases;
possibly, means for injecting the comburent in order to carry out the post-combustion of the process gases;
a tap hole for the transformed material and the slags yielded;
possibly, means for feeding the stirring gas onto the reactor bottom.
The means for the joint and concomitant feeding of the material to be transformed, the fuel, the comburent and the additives to the bottom portion of the reactor may be nozzles, circumferentially arranged, horizontal or slanting downwards, and oriented centerwise, and possibly of at least one lance, vertically arranged so as to directly inject into the molten slag.
Said nozzles may be slanting downwards of an angle ranging from 0 to 40xc2x0 with respect to the horizontal plane.
The ratio between the inside height and the inside diameter of the cylindrical chamber, reactor, may range from 1 to 8.
The ratio between the heights of the frustoconical-shaped connector and of the reactor may range from 0.2 to 0.5. The means for feeding the stirring gas into the reactor may be porous baffles located onto the bottom thereof.
The cylindrical top portion of the reactor may be differentially cooled along the height thereof.
The materials to be thermally destroyed, gasified, inertized, or from which products of commercial value are to be recovered are inletted into the reactor, in the portion thereof with the molten slag bath, through a plurality of nozzles, and possibly carried by a material-carrying gas, concomitantly and jointly to the slag additives and inoculants (like, e.g., calcium or magnesium oxides or carbonates), possibly highly reducing metals (like, e.g., aluminium, magnesium), fuel (like pit coal, fuel oil, natural gas or binary or ternary mixtures thereof) and to the comburent (like air, oxygen or a mixture thereof).
The material inletted into the slag meets an elevated temperature environment which, owing to the presence of the fuel carbon and of the carbon monoxide evolved from the partial burning of the fuel with the comburent gas, and to that of possible injected reducing metals, is highly reducing.
All the above leads to a ready reduction of the reducible metallic oxides, like iron, chromium, nickel and lead oxides, and to the evaporation of volatile metals like zinc, lead and cadmium.
The presence of calcium oxide in the slag and the highly reducing environment, needwise enhanced by the reducing metals injected therein, entails that the harmful elements (like, e.g., sulfur and halogens) be incorporated in the slag essentially as calcium salts; the reducing environment avoids the formation of NOx in the process flue gases.
The non-reducible oxides, like CaO, MgO, SiO2, Al2O3, are completely incorporated, since they dissolve in the slag.
The direct gasification under reducing conditions of the injected carbon-containing materials provides CO; further CO may evolve from the reduction of metallic oxides by the slag-dispersed carbon; the process gas thus evolved may possibly be post-combusted, in order to sustain the thermal state of the reactor, even injecting comburent therein through upperly located nozzles.
The processes implementable according to the present invention in view of the aims thereof require elevated reaction kinetics, depending also on an adequate homogeneity of the bath (made of metallic and of slag phases), and efficient heat exchanges, aims to be attained with a intensive bath stirring.
The bath stirring is essentially carried out by the materials injected with the abovementioned nozzles, and possibly by blowing gas from the reactor bottom.
Hence, the apparatus subject-matter of the present invention provides elevated operative flexibility and specific productivity.